1. Technological Field
This technical disclosure pertains generally to making non-reciprocal components utilizing distributed modulated capacitors (DMC), and more particularly to DMC circulators for allowing microwave signals to travel in opposite directions along the same path and be readily separated.
2. Background Discussion
It is well known that based on the reciprocity theorem, non-reciprocity cannot be realized in a lossless form if the component is made of only linear, passive, reciprocal material. Non-reciprocal microwave components, such as isolators and circulators, require the use of non-reciprocal material, for example ferrite magnetic material. These components, however, are often bulky, lossy and narrow band, particularly when they are operated at the lower end of the microwave frequency spectrum.
Separating a transmitting and receiving channel connected to a single antenna is currently realized with circulators which are often fabricated using non-reciprocal magnetic material, such as ferrite. They are not compatible with the standard integrated circuit process and can provide good performance over only a relatively narrow band. Circulators based on optical links can offer broadband performance, however, they are physically bulky and cannot be integrated on-chip either. Active circulators based on transistor amplifiers have also been developed, but these devices add noise to the receiver, while the use of these active devices limits the maximum operating power of the transmitter.
Accordingly, a need exists for apparatus and methods for realizing non-reciprocal components without the limitation of previous techniques.